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Renewable Energy and Utility System Optimization for Sustainable Industries

A special issue of Sustainability (ISSN 2071-1050). This special issue belongs to the section "Energy Sustainability".

Deadline for manuscript submissions: closed (28 February 2025) | Viewed by 71250

Special Issue Editors


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Guest Editor
School of Computing, Engineering and Physical Sciences, University of the West of Scotland, Paisley, PA1 2BE, UK
Interests: biomass; biofuels; renewable energy; microalgae
School of Computing, Engineering and Physical Sciences, University of the West of Scotland, Paisley, PA1 2BE, UK
Interests: whole site system optimisation and scheduling; system reliability and availability analysis; waste heat recovery

Special Issue Information

Dear Colleagues,

The integration of new renewable energy systems and utility system optimization are two ways of improving the sustainable performance of industrial processes. The environmental and economic sustainability of industries greatly depends on the source and use of energy and the optimization of the multiple utilities. This Special Issue invites novel contributions and comprehensive reviews covering all aspects of sustainable industries; focused but not limited to the following:

  • Bioenergy in industry
  • Energy optimization
  • Waste heat recovery
  • Decarbonization
  • Pinch analysis
  • Machine learning for system optimization
  • System reliability, availability, and maintainability (RAM) analysis
  • System optimization and scheduling

Dr. Cristina Rodriguez
Dr. Li Sun
Guest Editors

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Keywords

  • bioenergy
  • renewable energy
  • energy optimization
  • waste heat recovery
  • sustainable development
  • decarbonization
  • pinch analysis
  • machine learning
  • system optimization and scheduling
  • carbon footprint
  • RAM

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Published Papers (15 papers)

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22 pages, 5905 KiB  
Article
Hybrid ANFIS-PI-Based Optimization for Improved Power Conversion in DFIG Wind Turbine
by Farhat Nasim, Shahida Khatoon, Ibraheem, Shabana Urooj, Mohammad Shahid, Asmaa Ali and Nidal Nasser
Sustainability 2025, 17(6), 2454; https://doi.org/10.3390/su17062454 (registering DOI) - 11 Mar 2025
Abstract
Wind energy is essential for promoting sustainability and renewable power solutions. However, ensuring stability and consistent performance in DFIG-based wind turbine systems (WTSs) remains challenging due to rapid wind speed variations, grid disturbances, and parameter uncertainties. These fluctuations result in power instability, increased [...] Read more.
Wind energy is essential for promoting sustainability and renewable power solutions. However, ensuring stability and consistent performance in DFIG-based wind turbine systems (WTSs) remains challenging due to rapid wind speed variations, grid disturbances, and parameter uncertainties. These fluctuations result in power instability, increased overshoot, and prolonged settling times, negatively impacting grid compliance and system efficiency. Conventional proportional-integral (PI) controllers are simple and effective in steady-state conditions, but they lack adaptability in dynamic situations. Similarly, artificial intelligence (AI)-based controllers, such as fuzzy logic controllers (FLCs) and artificial neural networks (ANNs), improve adaptability but suffer from high computational demands and training complexity. To address these limitations, this paper presents a hybrid adaptive neuro-fuzzy inference system (ANFIS)-PI controller for DFIG-based WTS. The proposed controller integrates fuzzy logic adaptability with neural network-based learning, allowing real-time optimization of control parameters. Implemented within the rotor-side converter (RSC) and grid-side converter (GSC), ANFIS enhances reactive power management, grid compliance, and overall system stability. The system was tested under a step wind speed signal varying from 10 m/s to 12 m/s to evaluate its robustness. The simulation results confirmed that the ANFIS-PI controller significantly improved performance compared with the conventional PI controller. Specifically, it reduced rotor speed overshoot by 3%, torque overshoot by 12.5%, active power overshoot by 2%, and DC link voltage overshoot by 20%. Additionally, the ANFIS-PI controller shortened settling time by 50% for rotor speed, by 25% for torque, by 33% for active power, and by 16.7% for DC link voltage, ensuring faster stabilization, enhanced dynamic response, and greater efficiency. These improvements establish the ANFIS-PI controller as an advanced, computationally efficient, and scalable solution for enhancing the reliability of DFIG-based WTS, facilitating seamless integration of wind energy into modern power grids. Full article
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<p>The architecture of the proposed grid-tied DFIG-based WECS.</p>
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<p>Power coefficient (<span class="html-italic">C</span><span class="html-italic">p</span>) versus tip speed ratio (λ) for WTS [<a href="#B29-sustainability-17-02454" class="html-bibr">29</a>].</p>
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<p>Power operating regions of WTS.</p>
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<p>(<b>a</b>,<b>b</b>) DFIG dq equivalent circuit.</p>
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<p>Basic structure of ANFIS.</p>
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<p>Flow chart of designing the ANFIS controller.</p>
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<p>Implementation of ANFIS controller in the rotor-side converter.</p>
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<p>Implementation of the ANFIS controller in the grid-side converter.</p>
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<p>Error reduction in RSC after 25 iterations.</p>
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<p>Error reduction in GSC after 25 iterations.</p>
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<p>ANFIS model structure.</p>
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<p>A test signal was applied to the signal builder of the proposed model.</p>
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<p>Hybrid and PI controllers’ responses for rotor speed.</p>
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<p>Hybrid and PI controllers’ responses for torque.</p>
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<p>Hybrid and PI controllers’ responses for active power.</p>
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<p>Hybrid and PI controllers’ responses for DC link voltage.</p>
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21 pages, 2801 KiB  
Article
Optimization of Solar-Assisted CCHP Systems: Enhancing Efficiency and Reducing Emissions Through Harris Hawks-Based Mathematical Modeling
by Uchechi Ukaegbu, Lagouge Tartibu and C. W. Lim
Sustainability 2024, 16(23), 10694; https://doi.org/10.3390/su162310694 - 6 Dec 2024
Viewed by 768
Abstract
The increasing demand for energy, driven by technological advances, population growth, and economic expansion, has intensified the focus on efficient energy management. Tri-generation systems, such as Combined Cooling, Heating, and Power (CCHP) systems, are of particular interest due to their efficiency and sustainability. [...] Read more.
The increasing demand for energy, driven by technological advances, population growth, and economic expansion, has intensified the focus on efficient energy management. Tri-generation systems, such as Combined Cooling, Heating, and Power (CCHP) systems, are of particular interest due to their efficiency and sustainability. Integrating renewable energy sources like solar power with traditional fossil fuels further optimizes CCHP systems. This study presents a novel method for enhancing the CCHP system efficiency by identifying the optimal design parameters and assisting decision makers in selecting the best geometric configurations. A mathematical programming model using the Harris Hawks optimizer was developed to maximize the net power and exergy efficiency while minimizing CO2 emissions in a solar-assisted CCHP system. The optimization resulted in 100 Pareto optimal solutions, offering various choices for performance improvement. This method achieved a higher net power output, satisfactory exergy efficiency, and lower CO2 emissions compared to similar studies. The study shows that the maximum net power and exergy efficiency, with reduced CO2 emissions, can be achieved with a system having a low compression ratio and low combustion chamber inlet temperature. The proposed approach surpassed the response surface method, achieving at least a 4.2% reduction in CO2 emissions and improved exergy values. Full article
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<p>An illustration of the solar-assisted CCHP system.</p>
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<p>Flowchart for single-objective Harris Hawks optimization.</p>
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<p>Flowchart for multi-objective Harris Hawks optimization.</p>
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<p>Pareto front illustrating the relationship between CO<sub>2</sub> emissions, net power, and exergy efficiency.</p>
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<p>Pareto front showing the trade-off between CO<sub>2</sub> emissions and net power.</p>
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<p>Pareto front showing the trade-off between exergy efficiency and CO<sub>2</sub> emissions.</p>
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<p>Pareto front showing the trade-off between exergy efficiency and net power.</p>
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<p>Scatter pattern of decision variables.</p>
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21 pages, 392 KiB  
Article
Decarbonizing Public Transportation: A Multi-Criteria Comparative Analysis of Battery Electric Buses and Fuel Cell Electric Buses
by Afnan Fayez Eliyan, Mohamed Haouari and Ahmad Sleiti
Sustainability 2024, 16(21), 9354; https://doi.org/10.3390/su16219354 - 28 Oct 2024
Cited by 2 | Viewed by 1606
Abstract
To combat global warming, many industrialized countries have announced plans to ban vehicles powered by fossil fuel in the near future. In alignment with this global initiative, many countries across the globe are committed to decarbonizing their public transportation sector, which significantly contributes [...] Read more.
To combat global warming, many industrialized countries have announced plans to ban vehicles powered by fossil fuel in the near future. In alignment with this global initiative, many countries across the globe are committed to decarbonizing their public transportation sector, which significantly contributes to increased greenhouse gas emissions. A promising strategy to achieve this goal is the adoption of electric buses, specifically battery electric buses and fuel cell electric buses. Each technology offers distinct advantages and drawbacks, making the decision-making process complex. This research aims to answer two critical questions: What is the optimal choice for decarbonizing the bus transportation sector—electric battery buses or fuel cell electric buses? And what are the best energy carrier pathways for charging or refueling these buses? We propose a methodological framework based on multi-criteria decision-making to address these questions comprehensively. This framework utilizes the entropy weighting and the Technique for Order Preference by Similarity to the Ideal Solution (TOPSIS) methodologies to rank alternative bus technologies along with energy carrier pathways. The framework evaluates a range of criteria, including economic viability, energy demand, and environmental aspects. To illustrate the framework, we considered Qatar as a case study. Our results indicate that, with respect to economic viability and energy consumption, the operation of battery electric buses is favored over fuel cell electric buses, regardless of the energy pathway utilized during both the energy production and bus operation phases. However, from an environmental perspective, operating both bus alternatives using energy from green sources provides superior performance compared to when these buses are powered by natural gas sources. Full article
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<p>Methodological framework.</p>
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<p>Economic performance of the considered alternatives.</p>
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<p>WTW energy consumption.</p>
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<p>GWP (bar chart—left axis) and potential to change GWP (line plot—right axis) compared to the BEBs-NG baseline.</p>
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21 pages, 1922 KiB  
Article
A Two-Stage Evaluation of China’s New Energy Industrial Policy Package
by Qiao Wang, Shiyun Chen and Hongtao Yi
Sustainability 2024, 16(18), 8264; https://doi.org/10.3390/su16188264 - 23 Sep 2024
Viewed by 1128
Abstract
Energy structural transformation plays a strategically important role in achieving the dual-carbon reduction goals. Among the various approaches to carbon reduction, the Chinese government regards the growth of the new energy industry as an essential means. Considering that the government policy support determines [...] Read more.
Energy structural transformation plays a strategically important role in achieving the dual-carbon reduction goals. Among the various approaches to carbon reduction, the Chinese government regards the growth of the new energy industry as an essential means. Considering that the government policy support determines the long-term growth of the new energy industry, how to improve and optimize the policy support system has always been the core issue. Based on the fact that policy evaluation is a prerequisite, and the new energy industrial development requires the government to promote solutions in the form of a policy package rather than just individual policies, we investigate whether the implementation of the new energy industry policy package (NEIPP) is effective through an empirical case study of Shanghai. A two-stage evaluation method, which integrates the content analysis method (CAM) and synthetic control method (SCM), was used to empirically evaluate the actual effect of the NEIPP. At Stage One, four policy goals were summarized. SCM was used to identify the pure multi-effect of the NEIPP. The results showed that the NEIPP had a significant positive effect on green economic growth and industrial structure, while having a negative effect on carbon emissions. The NEIPP had no impact on the promotion of technological innovation. Several policy implications were drawn from this study. Full article
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<p>Refinement process of the NEIPP.</p>
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<p>Process of NEI policy text collection.</p>
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<p>Impact of the NEIPP on the real Shanghai’s technological innovation in contrast with the synthetic Shanghai: (<b>a</b>) Comparison of green technology innovation between real Shanghai and synthetic Shanghai: (<b>b</b>) Mean value gap between real Shanghai and synthetic Shanghai in green technology innovation.</p>
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<p>Impact of the NEIPP on the real Shanghai’s eEconomic sSustainable dDevelopment in contrast with the synthetic Shanghai: (<b>a</b>) Comparison of economic sustainable development between real Shanghai and synthetic Shanghai; (<b>b</b>) Mean value gap between real Shanghai and synthetic Shanghai in economic sustainable development.</p>
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<p>Impact of the NEIPP on the real Shanghai’s eEnergy sSaving and eEmission rReduction in contrast with the synthetic Shanghai: (<b>a</b>) Comparison of energy saving and emission reduction between real Shanghai and synthetic Shanghai; (<b>b</b>) Mean value gap between real Shanghai and synthetic Shanghai in energy saving and emission reduction.</p>
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<p>Impact of the NEIPP on the real Shanghai’s Industrial Structure Optimization in contrast with the synthetic Shanghai: (<b>a</b>) Comparison of industrial structure optimization between real Shanghai and synthetic Shanghai; (<b>b</b>) Mean value gap between real Shanghai and synthetic Shanghai in industrial structure organization.</p>
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<p>Distribution of differences by province and city: (<b>a</b>) Distribution of differences in green technological innovation by province (city); (<b>b</b>) Distribution of differences in economic sustainable development by province (city); (<b>c</b>) Distribution of differences in energy saving and emission reduction by province (city); (<b>d</b>) Distribution of differences in industrial structure optimization by province (city).</p>
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21 pages, 635 KiB  
Article
Cold Chain Distribution Route Optimization for Mixed Vehicle Types of Fresh Agricultural Products Considering Carbon Emissions: A Study Based on a Survey in China
by Shuangli Pan, Huiyu Liao, Guijun Zheng, Qian Huang and Maozhuo Shan
Sustainability 2024, 16(18), 8207; https://doi.org/10.3390/su16188207 - 20 Sep 2024
Viewed by 1329
Abstract
With the improvement of people’s living standards and the widening of circulation channels, the demand for fresh agricultural products continues to increase. The increase in demand will lead to an increase in delivery vehicles, costs, and carbon emissions, among which the increase in [...] Read more.
With the improvement of people’s living standards and the widening of circulation channels, the demand for fresh agricultural products continues to increase. The increase in demand will lead to an increase in delivery vehicles, costs, and carbon emissions, among which the increase in carbon emissions will aggravate pollution and is not conducive to sustainable development. Therefore, it is very important to balance economic and environmental benefits in the distribution of fresh agricultural products. Based on the analysis of the distribution characteristics of fresh agricultural products, this paper studies the optimization of the cold chain distribution route of fresh agricultural products considering carbon emission. Firstly, the cold chain distribution route planning of fresh agricultural products was investigated and analyzed by the interview method, and the basis for establishing the model objective and constraint conditions was obtained. Then, taking the minimum total cost including carbon emission cost as the optimization goal, the cold chain distribution route optimization model for mixed vehicle types is established considering electric refrigerated vehicles, gasoline refrigerated vehicles, and so on. Genetic algorithm was used to solve the model, and MATLAB2018b was used to substitute specific case data for simulation analysis. The analysis results show that increasing the consideration of carbon emission and mixed vehicle types in the distribution route of fresh agricultural products can not only reduce the distribution cost but also reduce the carbon emission. To some extent, the research content of this paper can provide a reference for enterprises in planning cold chain distribution routes of fresh agricultural products. Full article
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<p>Genetic algorithm operation steps.</p>
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<p>Diagram of single-point crossover.</p>
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24 pages, 4384 KiB  
Article
Optimisation of Process Parameters to Maximise the Oil Yield from Pyrolysis of Mixed Waste Plastics
by Farjana Faisal, Mohammad Golam Rasul, Ashfaque Ahmed Chowdhury and Md Islam Jahirul
Sustainability 2024, 16(7), 2619; https://doi.org/10.3390/su16072619 - 22 Mar 2024
Cited by 3 | Viewed by 2930
Abstract
The study sought to optimise process parameters of thermal pyrolysis of mixed waste plastic (MWP) to maximise pyrolytic oil yield. High-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS) were used as feedstocks for pyrolysis. Response surface methodology (RSM) and Box–Behnken design (BBD) were [...] Read more.
The study sought to optimise process parameters of thermal pyrolysis of mixed waste plastic (MWP) to maximise pyrolytic oil yield. High-density polyethylene (HDPE), polypropylene (PP), and polystyrene (PS) were used as feedstocks for pyrolysis. Response surface methodology (RSM) and Box–Behnken design (BBD) were used to optimise the pyrolysis process. The optimisation was carried out by varying three independent variables, namely, reaction temperature (460–540 °C), residence time (30–150 min), and size of MWP feedstock (5–45 mm), to increase the liquid oil yield. A BBD matrix was used to generate the design of the experiments, and 15 experiments were conducted. The highest liquid oil yield of 75.14 wt% was obtained by optimising the operating parameters, which were a reaction temperature of 535.96 °C, a reaction time of 150 min, and a feedstock particle size of 23.99 mm. A model was developed to determine the relationships among the independent variables, and analysis of variance (ANOVA) was used to investigate their impact on maximising oil yield. ANOVA results showed that the temperature and residence time had the maximum impact on oil yield, followed by feedstock size. Physicochemical analysis of the properties of the plastic pyrolytic oil (PPO) revealed that the crude PPO obtained from the MWP had higher water (0.125 wt%) and sulfur content (5.12 mg/kg) and lower flash point (<20 °C) and cetane index (32), which makes it unsuitable for use as an automobile fuel. However, these issues can be resolved by upgrading the PPO using different posttreatment techniques, such as distillation and hydrotreatment. Full article
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<p>Shredded waste plastic feedstocks: (<b>a</b>) PP, (<b>b</b>) HDPE, (<b>c</b>) PS, and (<b>d</b>) shredder.</p>
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<p>MWP feedstocks of three different sizes: 5 mm, 25 mm, and 45 mm.</p>
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<p>(<b>a</b>) Plastic pyrolytic plant, (<b>b</b>) process schematic diagram.</p>
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<p>Flow diagram of the processes of RSM for model development and validation.</p>
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<p>Experimental vs. predicted yield of PPO.</p>
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<p>(<b>a</b>) The 3D surface and (<b>b</b>) contour plot for PPO yield illustrate the combined impact of temperature and residence time while maintaining a constant feedstock particle size of 25 mm.</p>
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<p>(<b>a</b>) The 3D surface and (<b>b</b>) contour plot for PPO yield showing the combined effect of temperature and feedstock particle size, keeping residence time fixed at mean value (90 min).</p>
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<p>(<b>a</b>) The 3D surface and (<b>b</b>) contour plot for PPO yield showing the combined effect of temperature and feedstock particle size, keeping residence time fixed at mean value (90 min).</p>
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<p>(<b>a</b>) The 3D surface and (<b>b</b>) contour plot for PPO yield, while maintaining the temperature constant at 500 °C, demonstrating the combined impact of residence time and feedstock particle size.</p>
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<p>(<b>a</b>) The 3D surface and (<b>b</b>) contour plot for PPO yield, while maintaining the temperature constant at 500 °C, demonstrating the combined impact of residence time and feedstock particle size.</p>
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<p>FTIR spectra of PPO under optimum conditions.</p>
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19 pages, 3721 KiB  
Article
System Design, Optimization and 2nd Law Analysis of a 100 MWe Double Reheat s-CO2 Power Plant at Full Load and Part Loads
by Sreekanth Manavalla, Feroskhan M., Joseph Daniel, Sivakumar Ramasamy, T. M. Yunus Khan, Rahmath Ulla Baig, Naif Almakayeel and Bhanu Kiran Voddin Tirumalapur
Sustainability 2023, 15(20), 14677; https://doi.org/10.3390/su152014677 - 10 Oct 2023
Viewed by 1253
Abstract
Super-critical Carbon dioxide (s-CO2) power plants are considered to be efficient and environmentally friendly compared to the traditional Rankine cycle-based steam power plants and Brayton cycle-based gas turbine power plants. In this work, the system design of a coal-fired 100 MWe [...] Read more.
Super-critical Carbon dioxide (s-CO2) power plants are considered to be efficient and environmentally friendly compared to the traditional Rankine cycle-based steam power plants and Brayton cycle-based gas turbine power plants. In this work, the system design of a coal-fired 100 MWe double reheat s-CO2 power plant is presented. The system is also optimized for efficiency with turbine inlet pressures and the recompression ratio as the variables. The components needed, mass flow rates of various streams and their pressures at various locations in the system have been established. The plant has been studied based on 1st and 2nd laws at full load and at part loads of 80%, 60% and 40%. Operating parameters such as mass flow rate, pressure and temperature have considerably changed in comparison to full load operation. It was also observed that the 1st law efficiency is 53.96%, 53.93%, 52.63% and 50% while the 2nd law efficiency is 51.88%, 51.86%, 50.61% and 48.1% at 100%, 80%, 60% and 40% loads, respectively. The power plant demonstrated good performance even at part loads, especially at 80% load, while the performance deteriorated at lower loads. At full load, the highest amount of exergy destruction is found in the main heater (36.6%) and re-heaters (23.2% and 19.6%) followed by the high-temperature recuperator (5.7%) and cooler (4.1%). Similar trends were observed for the part load operation. It has been found that the recompression ratio should be kept high (>0.5) at lower loads in order to match the performance at higher loads. Combustion and heat exchange due to finite temperature differences are the main causes of exergy destruction, followed by pressure drop. Full article
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<p>Schematic layout of the double reheat recompression s-CO<sub>2</sub> power generation system.</p>
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<p>Temperature–Entropy diagram of the double reheat recompression s-CO<sub>2</sub> plant at full load.</p>
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<p>Values of pressure, temperature, enthalpy and mass flow rates at various locations in the double reheat 100 MW<sub>e</sub> s-CO<sub>2</sub> power plant. The major legend is to be read as shown here <span class="html-fig-inline" id="sustainability-15-14677-i001"><img alt="Sustainability 15 14677 i001" src="/sustainability/sustainability-15-14677/article_deploy/html/images/sustainability-15-14677-i001.png"/></span>.</p>
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<p>Exergy flow in the full load (100 MWe) plant.</p>
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<p>Influence of recompression ratio on 1st law efficiency.</p>
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<p>Percentage of exergy lost in various components.</p>
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<p>Value diagram of (<b>a</b>) HT recuperator, (<b>b</b>) LT recuperator and (<b>c</b>) Cooler.</p>
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<p>Specific work as a function of recompression ratio at various loads.</p>
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<p>Comparison of 1st and 2nd law efficiencies at various loads.</p>
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13 pages, 2006 KiB  
Article
Optimal Parameter Determination of Membrane Bioreactor to Boost Biohydrogen Production-Based Integration of ANFIS Modeling and Honey Badger Algorithm
by Hegazy Rezk, A. G. Olabi, Mohammad Ali Abdelkareem, Abdul Hai Alami and Enas Taha Sayed
Sustainability 2023, 15(2), 1589; https://doi.org/10.3390/su15021589 - 13 Jan 2023
Cited by 6 | Viewed by 1930
Abstract
Hydrogen is a new promising energy source. Three operating parameters, including inlet gas flow rate, pH and impeller speed, mainly determine the biohydrogen production from membrane bioreactor. The work aims to boost biohydrogen production by determining the optimal values of the control parameters. [...] Read more.
Hydrogen is a new promising energy source. Three operating parameters, including inlet gas flow rate, pH and impeller speed, mainly determine the biohydrogen production from membrane bioreactor. The work aims to boost biohydrogen production by determining the optimal values of the control parameters. The proposed methodology contains two parts: modeling and parameter estimation. A robust ANIFS model to simulate a membrane bioreactor has been constructed for the modeling stage. Compared with RMS, thanks to ANFIS, the RMSE decreased from 2.89 using ANOVA to 0.0183 using ANFIS. Capturing the proper correlation between the inputs and output of the membrane bioreactor process system encourages the constructed ANFIS model to predict the output performance exactly. Then, the optimal operating parameters were identified using the honey badger algorithm. During the optimization process, inlet gas flow rate, pH and impeller speed are used as decision variables, whereas the biohydrogen production is the objective function required to be maximum. The integration between ANFIS and HBA boosted the hydrogen production yield from 23.8 L to 25.52 L, increasing by 7.22%. Full article
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<p>Arrangement of ANFIS model for membrane bioreactor.</p>
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<p>Membership functions of ANFIS model for membrane bioreactor.</p>
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<p>Three-dimensional plot of controlling parameters; (<b>a</b>) flow rat and pH, (<b>b</b>) pH and impeller speed and (<b>c</b>) impeller speed and the flow rate.</p>
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<p>Predicted versus CFD data of ANFIS model.</p>
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<p>Prediction accuracy of ANFIS model.</p>
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<p>Particle movement during the identification procedure (<b>a</b>) hydrogen production, (<b>b</b>) normalized pH, (<b>c</b>) normalized flow rate and (<b>d</b>) normalized impeller speed.</p>
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22 pages, 11976 KiB  
Article
A Comparison of Different Renewable-Based DC Microgrid Energy Management Strategies for Commercial Buildings Applications
by Hegazy Rezk, Rania M. Ghoniem, Seydali Ferahtia, Ahmed Fathy, Mohamed M. Ghoniem and Reem Alkanhel
Sustainability 2022, 14(24), 16656; https://doi.org/10.3390/su142416656 - 12 Dec 2022
Cited by 4 | Viewed by 1967
Abstract
DC microgrid systems allow commercial buildings to use locally generated energy and achieve an optimal economy efficiently. Economical and eco-friendly energy can be achieved by employing renewable energy sources. However, additional controllable sources, such as fuel cells, are required because of their reduced [...] Read more.
DC microgrid systems allow commercial buildings to use locally generated energy and achieve an optimal economy efficiently. Economical and eco-friendly energy can be achieved by employing renewable energy sources. However, additional controllable sources, such as fuel cells, are required because of their reduced efficiency and fluctuated nature. This microgrid can use energy storage systems to supply transient power and enhance stability. The functioning of the microgrid and its efficiency are related to the implemented energy management strategy. In this paper, a comparison of several reported energy management strategies is fulfilled. The considered EMSs include the fuzzy logic control (FLC) strategy, the state machine control (SMC) strategy, the equivalent consumption minimization strategy (ECMS), and external energy maximization strategy (EEMS). These strategies are compared in terms of power-saving, system efficiency, and power quality specifications. The overall results confirm the ability of EEMS (high efficiency of 84.91% and economic power-saving 6.11%) and SMC (efficiency of 84.18% with high power-saving 5.07%) for stationary applications, such as building commercial applications. These strategies provide other advantages, which are discussed in detail in this paper. Full article
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<p>The architecture of the proposed DC microgrid, where all the power sources are connected to the DC bus using their converters.</p>
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<p>PV equivalent circuit.</p>
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<p>Li-ion battery equivalent circuit.</p>
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<p>V-I and P-I characteristics curves.</p>
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<p>SOFC equivalent circuit.</p>
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<p>An illustration of the global EMS scheme.</p>
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<p>Membership functions for the first input (net power).</p>
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<p>Membership functions for the second input (SoC).</p>
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<p>The output surface for the fuzzy inference system.</p>
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<p>The generation of FC power reference using ECMS.</p>
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<p>The generation of FC power reference using EEMS.</p>
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<p>Illustration of the SMC control scheme states.</p>
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<p>Grid connector block scheme.</p>
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<p>The proposed DC Bus stabilization control scheme.</p>
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<p>Solar irradiance profile for five days (W/m<sup>2</sup>) [<a href="#B32-sustainability-14-16656" class="html-bibr">32</a>].</p>
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<p>Used load and solar power profiles for five days (kW) [<a href="#B32-sustainability-14-16656" class="html-bibr">32</a>].</p>
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<p>The measured load, the renewable, and the net power (kW).</p>
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<p>FC, battery, and grid power using EEMS (kW).</p>
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<p>FC, battery, and grid power using ECMS (kW).</p>
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<p>FC, battery, and grid power using SMC (kW).</p>
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<p>FC, battery, and grid power using FLC-based EMS (kW).</p>
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<p>Battery State of Charge (%).</p>
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<p>Simulation Statistics.</p>
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<p>DC bus voltage (V).</p>
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<p>Bus voltage graphical statistics.</p>
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25 pages, 9868 KiB  
Article
A New Fractional-Order Load Frequency Control for Multi-Renewable Energy Interconnected Plants Using Skill Optimization Algorithm
by Ahmed Fathy, Hegazy Rezk, Seydali Ferahtia, Rania M. Ghoniem, Reem Alkanhel and Mohamed M. Ghoniem
Sustainability 2022, 14(22), 14999; https://doi.org/10.3390/su142214999 - 13 Nov 2022
Cited by 18 | Viewed by 2374
Abstract
Connection between electric power networks is essential to cover any deficit in the generation of power from any of them. The exchange powers of the plants during load disturbance should not be violated beyond their specified values. This can be achieved by installing [...] Read more.
Connection between electric power networks is essential to cover any deficit in the generation of power from any of them. The exchange powers of the plants during load disturbance should not be violated beyond their specified values. This can be achieved by installing load frequency control (LFC); therefore, this paper proposes a new metaheuristic-based approach using a skill optimization algorithm (SOA) to design a fractional-order proportional integral derivative (FOPID)-LFC approach with multi-interconnected systems. The target is minimizing the integral time absolute error (ITAE) of frequency and exchange power violations. Two power systems are investigated. The first one has two connected plants of photovoltaic (PV) and thermal units. The second system contains four plants, namely, PV, wind turbine, and two thermal plants, with governor dead-band (GDB) and generation rate constraints (GRC). Different load disturbances are analyzed in both considered systems. Extensive comparisons to the use of chef-based optimization algorithm (CBOA), jumping spider optimization algorithm (JSOA), Bonobo optimization (BO), Tasmanian devil optimization (TDO), and Atomic orbital search (AOS) are conducted. Moreover, statistical tests of Friedman ANOVA table, Wilcoxon rank test, Friedman rank test, and Kruskal Wallis test are implemented. Regarding the two interconnected areas, the proposed SOA achieved the minimum fitness value of 1.8779 pu during 10% disturbance on thermal plant. In addition, it outperformed all other approaches in the case of 1% disturbance on the first area as it achieved ITAE of 0.0327 pu. The obtained results proved the competence and reliability of the proposed SOA in designing an efficient FOPID-LFC in multi-interconnected power systems with multiple sources. Full article
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<p>I-V and P-V characteristics of PV panel.</p>
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<p>WT output power versus the rotor speed.</p>
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<p>The considered PV/thermal connected power system.</p>
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<p>The architecture of thermal/WT/thermal/PV system.</p>
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<p>SOA flowchart.</p>
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<p>The configuration of a power plant with the proposed SOA-FOPID.</p>
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<p>PV/thermal system in Simulink.</p>
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<p>The fitness value versus the iteration number for PV/thermal system at ΔP<sub>L1</sub> = 10%.</p>
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<p>The time responses of (<b>a</b>) ΔF<sub>1</sub>, (<b>b</b>) ΔF<sub>2</sub>, and (<b>c</b>) ΔP<sub>tie</sub> for PV/thermal system at ΔP<sub>L1</sub> = 10%.</p>
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<p>The fitness functions during separate trials via ANOVA Wallis for PV/thermal system at ΔP<sub>L1</sub> = 10%.</p>
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<p>The fitness value versus the iteration number for PV/thermal system at ΔP<sub>L2</sub> = 10%.</p>
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<p>The time responses of (<b>a</b>) ΔF<sub>1</sub>, (<b>b</b>) ΔF<sub>2</sub>, and (<b>c</b>) ΔP<sub>tie</sub> for PV/thermal system at ΔP<sub>L2</sub> = 10%.</p>
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<p>The time responses of (<b>a</b>) ΔF<sub>1</sub>, (<b>b</b>) ΔF<sub>2</sub>, and (<b>c</b>) ΔP<sub>tie</sub> for PV/thermal system at ΔP<sub>L2</sub> = 10%.</p>
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<p>Simulink model of thermal/WT/thermal/PV interconnected system.</p>
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<p>The time responses of (<b>a</b>) ΔF<sub>1</sub>, ΔF<sub>2</sub> (<b>b</b>) ΔF<sub>3</sub>, ΔF<sub>4</sub>, (<b>c</b>) ΔP<sub>tie1</sub>, ΔP<sub>tie2,</sub> and (<b>d</b>) ΔP<sub>tie3</sub>, ΔP<sub>tie4</sub> of thermal/WT/thermal/PV system at ΔP<sub>L1</sub> = 1%.</p>
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<p>The time responses of (<b>a</b>) ΔF<sub>1</sub>, ΔF<sub>2</sub> (<b>b</b>) ΔF<sub>3</sub>, ΔF<sub>4</sub>, (<b>c</b>) ΔP<sub>tie1</sub>, ΔP<sub>tie2,</sub> and (<b>d</b>) ΔP<sub>tie3</sub>, ΔP<sub>tie4</sub> of thermal/WT/thermal/PV system at ΔP<sub>L1</sub> = 1%.</p>
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<p>Pattern of variable disturbance.</p>
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<p>The time responses of frequency and exchange power violations for thermal/WT/thermal/PV system with variable disturbance in area 1.</p>
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<p>The time responses of frequency and exchange power violations for thermal/WT/thermal/PV system with variable disturbance in area 1.</p>
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13 pages, 3058 KiB  
Article
Evaluation of Growth Rate and Biomass Productivity of Scenedesmus quadricauda and Chlorella vulgaris under Different LED Wavelengths and Photoperiods
by Ruth Chinyere Anyanwu, Cristina Rodriguez, Andy Durrant and Abdul Ghani Olabi
Sustainability 2022, 14(10), 6108; https://doi.org/10.3390/su14106108 - 17 May 2022
Cited by 20 | Viewed by 6487
Abstract
Cultivation has been identified as an essential stage for biofuel production. This research has examined two important parameters for the industrial production of microalgae, namely microalgae growth rate and biomass productivity. Chlorella vulgaris and Scenedesmusquadricauda were cultivated using a closed photobioreactor (PBR). [...] Read more.
Cultivation has been identified as an essential stage for biofuel production. This research has examined two important parameters for the industrial production of microalgae, namely microalgae growth rate and biomass productivity. Chlorella vulgaris and Scenedesmusquadricauda were cultivated using a closed photobioreactor (PBR). A novel approach for cultivation and energy input reduction was developed by incorporating periods of darkness during cultivation, as would happen in nature. Three different LED light sources (white, red, and green) were used to determine the conditions that result in the highest growth rate and biomass productivity. C. vulgaris and S. quadricauda responded differently to lighting conditions. It was found that, depending on the LED source and light period, different growth rates and biomass productivities were obtained. Overall, experimental results obtained in this study indicated that a white LED is more effective than green or red LEDs in increasing microalgae growth rate and biomass productivity. A maximum growth rate of 3.41 d−1 and a biomass productivity of 2.369 g L−1d−1 were achieved for S.quadricauda under a 19 h period of white light alternating with 5 h of darkness. For C. vulgaris the maximum growth rate of 3.49 d−1 and maximum biomass productivity of 2.438 g L−1d−1 were achieved by continuous white light with no darkness period. Full article
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<p>Closed PBR used in this research. (1) Tube head; (2) CO<sub>2</sub> tube; (3) LED lighting remote; (4) PBR outer cover; (5) pump for mixing; (6) handheld photometer.</p>
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<p>Microalgae species: (<b>a</b>) <span class="html-italic">C. vulgaris;</span> (<b>b</b>) <span class="html-italic">S. quadricauda</span>.</p>
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<p><span class="html-italic">C. vulgaris</span> growth curves under different lights at 24L:0D.</p>
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<p><span class="html-italic">S. quadricauda</span> growth curves under 24L:0D.</p>
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<p><span class="html-italic">S. quadricauda</span> growth curves under 19L:5D.</p>
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<p><span class="html-italic">C. vulgaris</span> growth curves under 19L:5D.</p>
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<p><span class="html-italic">C. vulgaris</span> growth curves under 12L:12D.</p>
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<p><span class="html-italic">S. quadricauda</span> growth curves under 12L:12D.</p>
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<p>Biomass productivity.</p>
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27 pages, 13580 KiB  
Article
Developing a Hybrid Approach Based on Analytical and Metaheuristic Optimization Algorithms for the Optimization of Renewable DG Allocation Considering Various Types of Loads
by Amal A. Mohamed, Salah Kamel, Ali Selim, Tahir Khurshaid and Sang-Bong Rhee
Sustainability 2021, 13(8), 4447; https://doi.org/10.3390/su13084447 - 16 Apr 2021
Cited by 11 | Viewed by 1918
Abstract
The optimal location of renewable distributed generations (DGs) into a radial distribution system (RDS) has attracted major concerns from power system researchers in the present years. The main target of DG integration is to improve the overall system performance by minimizing power losses [...] Read more.
The optimal location of renewable distributed generations (DGs) into a radial distribution system (RDS) has attracted major concerns from power system researchers in the present years. The main target of DG integration is to improve the overall system performance by minimizing power losses and improving the voltage profile. Hence, this paper proposed a hybrid approach between an analytical and metaheuristic optimization technique for the optimal allocation of DG in RDS, considering different types of load. A simple analytical technique was developed in order to determine the sizes of different and multiple DGs, and a new efficient metaheuristic technique known as the Salp Swarm Algorithm (SSA) was suggested in order to choose the best buses in the system, proportionate to the sizes determined by the analytical technique, in order to obtain the minimum losses and the best voltage profile. To verify the power of the proposed hybrid technique on the incorporation of the DGs in RDS, it was applied to different types of static loads; constant power (CP), constant impedance (CZ), and constant current (CI). The performance of the proposed algorithm was validated using two standards RDSs—IEEE 33-bus and IEEE 69-bus systems—and was compared with other optimization techniques. Full article
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<p>Two bus radial distribution network.</p>
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<p>(<b>a</b>) Individual salp; (<b>b</b>) swarm of salps (salps chain) [<a href="#B19-sustainability-13-04447" class="html-bibr">19</a>].</p>
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<p>Single line diagram of the 33-bus system.</p>
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<p>Single line diagram of the 69-bus system.</p>
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<p>Pl and Iter of DG type I for the three loads.</p>
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<p>Pl and Iter of DG type II for the three loads.</p>
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<p>Pl and Iter of DG type III for the three loads.</p>
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<p>Voltage profile of DG type I for the CP load.</p>
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<p>Voltage profile of DG type II for the CP load.</p>
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<p>Voltage profile of DG type III for the CP load.</p>
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<p>Voltage profile of DG type I for the CI load.</p>
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<p>Voltage profile of DG type II for the CI load.</p>
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<p>Voltage profile of DG type III for the CI load.</p>
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<p>Voltage profile of DG type I for the CZ load.</p>
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<p>Voltage profile of DG type II for the CZ load.</p>
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<p>Voltage profile of DG type III for the CZ load.</p>
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<p>The power loss of DG type I for the three loads.</p>
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<p>The power loss of DG type II for the three loads.</p>
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<p>The power loss of DG type III for the three loads.</p>
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<p>Pl and Iter of DG type I for the three loads.</p>
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<p>Pl and Iter of DG type II for the three loads.</p>
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<p>Pl and Iter of DG type III for the three loads.</p>
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<p>Voltage profile of DG type I for the CP load.</p>
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<p>Voltage profile of DG type II for the CP load.</p>
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<p>Voltage profile of DG type III for the CP load.</p>
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<p>Voltage profile of DG type I for the CI load.</p>
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<p>Voltage profile of DG type II for the CI load.</p>
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<p>Voltage profile of DG type III for the CI load.</p>
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<p>Voltage profile of DG type I for the CZ load.</p>
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<p>Voltage profile of DG type II for the CZ load.</p>
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<p>Voltage profile of DG type III for the CZ load.</p>
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<p>The power loss of DG type I for the three loads.</p>
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<p>The power loss of DG type II for the three loads.</p>
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<p>The power loss of DG type III for the three loads.</p>
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Review

Jump to: Research

22 pages, 4742 KiB  
Review
Wind Energy Contribution to the Sustainable Development Goals: Case Study on London Array
by A. G. Olabi, Khaled Obaideen, Mohammad Ali Abdelkareem, Maryam Nooman AlMallahi, Nabila Shehata, Abdul Hai Alami, Ayman Mdallal, Asma Ali Murah Hassan and Enas Taha Sayed
Sustainability 2023, 15(5), 4641; https://doi.org/10.3390/su15054641 - 6 Mar 2023
Cited by 68 | Viewed by 27456
Abstract
Clean and safe energy sources are essential for the long-term growth of society. Wind energy is rapidly expanding and contributes to many countries’ efforts to decrease greenhouse gas emissions. In terms of sustainable development goals (SDGs), renewable energy development promotes energy security while [...] Read more.
Clean and safe energy sources are essential for the long-term growth of society. Wind energy is rapidly expanding and contributes to many countries’ efforts to decrease greenhouse gas emissions. In terms of sustainable development goals (SDGs), renewable energy development promotes energy security while also facilitating community development and environmental conservation on a global scale. In this context, the current article aims to investigate wind energy’s role within the SDGs. Furthermore, the present study highlights the role of the London Array wind farm in achieving the SDGs. Indeed, deploying clean and economical energy sources in place of conventional fossil fuel power plants provides vital insights into environmental impacts. The London Array operation is saving approximately 1 million tons of carbon dioxide (CO2) equivalent. Furthermore, the London Array contributes to the achievement of multiple SDGs, including SDG 8: decent employment and economic growth; SDG 9: industry, innovation, and infrastructure; SDG 11: sustainable cities and communities; and SDG 15: life on land. To enhance the London Array’s contribution to the SDGs, a total of 77 indicators (key performance indicators) were proposed and compared to the current measurements that have been carried out. The results showed that the London Array used most of the suggested indicators without classifying them from the SDGs’ perspective. The proposed indicators will help cut operation costs, mitigate climate change and environmental damage, improve employee engagement and morale, reduce learning gaps, set goals and plans, and use resources efficiently. Full article
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<p>The United Nations Sustainable Development Goals (SDGs). (Open Access, <a href="https://www.un.org/development/desa/disabilities/envision2030.html" target="_blank">https://www.un.org/development/desa/disabilities/envision2030.html</a>, accessed on 1 November 2022).</p>
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<p>Wind energy capacity globally, data extracted from IRENA 2022 (<a href="https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2022/Apr/IRENA_RE_Capacity_Statistics_2022.pdf" target="_blank">https://www.irena.org/-/media/Files/IRENA/Agency/Publication/2022/Apr/IRENA_RE_Capacity_Statistics_2022.pdf</a>, accessed on 20 January 2022).</p>
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<p>Advantages and disadvantages of wind in the context of the SDGs.</p>
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<p>Contributions of wind energy in terms of social, economic, and environmental aspects.</p>
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<p>London Array project contributions to sustainable development.</p>
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<p>London Array’s contribution to the SDGs.</p>
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<p>Benefits of adopting the KPIs.</p>
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34 pages, 12871 KiB  
Review
Solar Energy: Applications, Trends Analysis, Bibliometric Analysis and Research Contribution to Sustainable Development Goals (SDGs)
by Khaled Obaideen, Abdul Ghani Olabi, Yaser Al Swailmeen, Nabila Shehata, Mohammad Ali Abdelkareem, Abdul Hai Alami, Cristina Rodriguez and Enas Taha Sayed
Sustainability 2023, 15(2), 1418; https://doi.org/10.3390/su15021418 - 11 Jan 2023
Cited by 96 | Viewed by 12226
Abstract
Over the past decade, energy demand has witnessed a drastic increase, mainly due to huge development in the industry sector and growing populations. This has led to the global utilization of renewable energy resources and technologies to meet this high demand, as fossil [...] Read more.
Over the past decade, energy demand has witnessed a drastic increase, mainly due to huge development in the industry sector and growing populations. This has led to the global utilization of renewable energy resources and technologies to meet this high demand, as fossil fuels are bound to end and are causing harm to the environment. Solar PV (photovoltaic) systems are a renewable energy technology that allows the utilization of solar energy directly from the sun to meet electricity demands. Solar PV has the potential to create a reliable, clean and stable energy systems for the future. This paper discusses the different types and generations of solar PV technologies available, as well as several important applications of solar PV systems, which are “Large-Scale Solar PV”, “Residential Solar PV”, “Green Hydrogen”, “Water Desalination” and “Transportation”. This paper also provides research on the number of solar papers and their applications that relate to the Sustainable Development Goals (SDGs) in the years between 2011 and 2021. A total of 126,513 papers were analyzed. The results show that 72% of these papers are within SDG 7: Affordable and Clean Energy. This shows that there is a lack of research in solar energy regarding the SDGs, especially SDG 1: No Poverty, SDG 4: Quality Education, SDG 5: Gender Equality, SDG 9: Industry, Innovation and Infrastructure, SDG 10: Reduced Inequality and SDG 16: Peace, Justice and Strong Institutions. More research is needed in these fields to create a sustainable world with solar PV technologies. Full article
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<p>Long-term average irradiance around planet earth (from <a href="http://www.smartenergyconsulting.com" target="_blank">www.smartenergyconsulting.com</a>, accessed on 13 July 2022).</p>
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<p>Schematic of an on-grid solar system.</p>
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<p>Main components of a solar power plant.</p>
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<p>Grid-connected solar rooftop system (from <a href="http://www.solarideatspl.com" target="_blank">www.solarideatspl.com</a>, accessed on 13 July 2022).</p>
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<p>Rooftop stand-alone PV system with batteries.</p>
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<p>Energy consumption of residential equipment in the UAE [<a href="#B71-sustainability-15-01418" class="html-bibr">71</a>], open access.</p>
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<p>Schematic of solar-powered air conditioner.</p>
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<p>Schematic of a solar-powered water pump.</p>
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<p>Types of energy storage routes.</p>
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<p>Simple water electrolysis.</p>
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<p>Schematic of solar–electrolyzer system with a storage tank [<a href="#B89-sustainability-15-01418" class="html-bibr">89</a>], open access.</p>
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<p>Schematic of solar water desalination system.</p>
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<p>Energy of internal combustion engine vehicles (ICEV) and battery electric vehicles (BEV) [<a href="#B107-sustainability-15-01418" class="html-bibr">107</a>], open access.</p>
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<p>Schematic of a solar charger for EVs.</p>
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<p>Data extraction process of “solar” from SCOPUS (<b>a</b>) and analysis of data process (<b>b</b>).</p>
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<p>Sustainable Development Goals (SDGs) (from <a href="http://www.sdgs.un.org" target="_blank">www.sdgs.un.org</a>, accessed on 13 July 2022).</p>
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<p>Solar papers regarding SDGs between 2011 and 2021.</p>
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<p>Solar SDG-related research papers by year: (<b>a</b>) SDG1, SDG 4, SDG 5 and SDG 16; (<b>b</b>) SDG2, SDG 8, SDG9 and SDG 10; (<b>c</b>) SDG3, SDG 7, SDG 12 and SDG 13; (<b>d</b>) SDG6, SDG 11, SDG 14 and SDG 15. A similar analysis, i.e., investigating the number of research papers related to SDGs, was conducted for the main five applications of solar (i.e., “Large-Scale Solar PV”, “Residential Solar PV”, “Green Hydrogen”, “Water De-salination” and “Transportation”). For application 1, which is large-scale solar PV power plants with a capacity of more than 1 MW, the total number of documents including SDGs was 4451 and was the highest among the five applications, and like the rest, SDG 7 had the highest percentage of documents with 84%. The second was SDG 13 with 6% of the total documents, and SDG 4 came last with zero documents.</p>
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<p>Solar energy and the three pillars of sustainable development.</p>
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<p>(<b>a</b>) Dashboard for solar; (<b>b</b>) Dashboard for large-scale solar power generation; (<b>c</b>) Dashboard for residential solar; (<b>d</b>) Dashboard for green hydrogen; (<b>e</b>) Dashboard for water desalination; (<b>f</b>) Dashboard for transportation.</p>
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<p>(<b>a</b>) Dashboard for solar; (<b>b</b>) Dashboard for large-scale solar power generation; (<b>c</b>) Dashboard for residential solar; (<b>d</b>) Dashboard for green hydrogen; (<b>e</b>) Dashboard for water desalination; (<b>f</b>) Dashboard for transportation.</p>
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<p>(<b>a</b>) Dashboard for solar; (<b>b</b>) Dashboard for large-scale solar power generation; (<b>c</b>) Dashboard for residential solar; (<b>d</b>) Dashboard for green hydrogen; (<b>e</b>) Dashboard for water desalination; (<b>f</b>) Dashboard for transportation.</p>
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<p>(<b>a</b>) Dashboard for solar; (<b>b</b>) Dashboard for large-scale solar power generation; (<b>c</b>) Dashboard for residential solar; (<b>d</b>) Dashboard for green hydrogen; (<b>e</b>) Dashboard for water desalination; (<b>f</b>) Dashboard for transportation.</p>
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<p>(<b>a</b>) Dashboard for solar; (<b>b</b>) Dashboard for large-scale solar power generation; (<b>c</b>) Dashboard for residential solar; (<b>d</b>) Dashboard for green hydrogen; (<b>e</b>) Dashboard for water desalination; (<b>f</b>) Dashboard for transportation.</p>
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<p>(<b>a</b>) Dashboard for solar; (<b>b</b>) Dashboard for large-scale solar power generation; (<b>c</b>) Dashboard for residential solar; (<b>d</b>) Dashboard for green hydrogen; (<b>e</b>) Dashboard for water desalination; (<b>f</b>) Dashboard for transportation.</p>
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30 pages, 2097 KiB  
Review
Sustainable Approaches to Microalgal Pre-Treatment Techniques for Biodiesel Production: A Review
by Amarnath Krishnamoorthy, Cristina Rodriguez and Andy Durrant
Sustainability 2022, 14(16), 9953; https://doi.org/10.3390/su14169953 - 11 Aug 2022
Cited by 24 | Viewed by 4474
Abstract
Microalgae are a potential source of numerous nutritional products and biofuels. Their applications range from the food industry to the medical and fuel sectors and beyond. Recently, the conversion of biomass into biodiesel and other biofuels has received a lot of positive attention [...] Read more.
Microalgae are a potential source of numerous nutritional products and biofuels. Their applications range from the food industry to the medical and fuel sectors and beyond. Recently, the conversion of biomass into biodiesel and other biofuels has received a lot of positive attention within the fossil fuel arena. The objective of biorefineries is to focus on utilising biomass efficiently to produce quality biofuel products by minimising the input as well as to reduce the use of chemical or thermal pre-treatments. Pre-treatment processes in biorefineries involve cell disruption to obtain lipids. Cell disruption is a crucial part of bioconversion, as the structure and nature of microalgae cell walls are complex. In recent years, many research papers have shown various pre-treatment methods and their advantages. The objective of this paper was to provide a comprehensive in-depth review of various recent pre-treatment techniques that have been used for microalgal biodiesel production and to discuss their advantages, disadvantages, and how they are applied in algal biorefineries. Full article
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<p>Approaches for converting microalgae to biodiesel.</p>
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<p>Schematic diagram of HPH value seat.</p>
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<p>Schematic view of a wet bead milling process [<a href="#B63-sustainability-14-09953" class="html-bibr">63</a>].</p>
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<p>Graphic showing <span class="html-italic">Scenedesmus obliquus</span> during ultrasonic pre-treatment [<a href="#B81-sustainability-14-09953" class="html-bibr">81</a>].</p>
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<p>Schematic representation of ultrasonic system: (a) transducer, (b) thermometer, (c) ultrasonic reactor, (d) cryostat, (e) ultrasonic generator [<a href="#B89-sustainability-14-09953" class="html-bibr">89</a>].</p>
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<p>Picture of microwave-assisted treatment for microalgae [<a href="#B93-sustainability-14-09953" class="html-bibr">93</a>].</p>
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<p>Schematic diagram of steam explosion and a fractionation reactor [<a href="#B109-sustainability-14-09953" class="html-bibr">109</a>].</p>
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<p>Schematic representation of lipid productivity of microalgae [<a href="#B54-sustainability-14-09953" class="html-bibr">54</a>].</p>
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